This application seeks support for research to address the problem of stimulus overselectivity as it may impact stimulus control in functional academics and augmentative/alternative communication (AAC). Overselectivity refers to maladaptive narrow attending that is a common learning problem in children with intellectual disabilities. Overselectivity is often associated with autism spectrum disorders (ASD), but the research foundation for this relation is inconclusive and largely based on procedures that fail to capture the complex and dynamic relational learning aspects of special-education curricula. Recent research has produced methodologies to study overselectivity in contexts that model teaching situations, as well as promising remedial procedures that can reduce or eliminate overselective attending by corrective therapy and/or behavioral prostheses. We propose a formal comparison of stimulus overselectivity in four study populations: MA- and CA-matched children with ASD, Down syndrome, and intellectual disabilities of mixed/unknown etiology; and MA-matched typically developing children. Tests will include stimuli developed for basic research, as well as stimulus sets of clinical/educational interest (AAC icons, photos of faces, and printed words). We will determine whether an ASD diagnosis is related to (1) increased prevalence or severity of overselective stimulus control; (2) a deficit in the disengagement of attention and/or indifference to perceptual coherence of stimuli; and (3) the effectiveness, durability, and net gain resulting from intervention and remedial training. We will also apply behavior-analytic quantitative models of attention (4) to determine whether strategic manipulations of reinforcement parameters can be used to identify and ameliorate overselectivity that emerges from attention biases interacting with the uncontrolled reinforcement contingencies of teaching procedures typically used in special-education settings. Finally, (5) we will conduct a series of applied studies to examine generalization and durability of remedial interventions for academic tasks in special-education classrooms. Results of the proposed studies will contribute to a better characterization of the learning problems associated with the study populations and to increased understanding of basic stimulus control processes in learning. Application of the resulting knowledge seems highly likely to improve current methods for teaching and evaluating individuals with intellectual disabilities.